The invention relates to fluid meters for measuring variable flow rates in a pipe using a high volume flow meter and a low volume flow meter, which together form what is referred to in the technical field as a xe2x80x9ccompound flow meter.xe2x80x9d
Examples of prior compound flow meters are seen in Bradham III, et al. U.S. Pat. No. 4,100,799, Pelt, U.S. Pat. No. 4,217,929, Kullmann et al., U.S. Pat. No. 4,429,571 and Karjalainefl, U.S. Pat. No. 4,437,344.
In a compound flow meter, a secondary flow passageway is typically provided for a low volume flow. This secondary flow passageway connects the primary flow passageway to a chamber in which a low volume flow meter, such as a nutating disc type meter, is situated to measure flow in the low flow range. A meter register is mechanically or magnetically coupled to the flow responsive element in the low volume flow meter to provide a readout of the flow rate in cubic feet, gallons, cubic meters, imperial gallons or other units. A pressure-responsive valve is situated in the main flow passageway, and when the flow exceeds a predetermined threshold, it forces open the valve door and the flow moves through the remaining portion of the main flow passageway in which a high volume flow meter, such as a turbine meter, is positioned. The flow responsive element of the high volume flow meter is also coupled to a meter register. When the flow drops to a certain level, which may be lower than the flow that was required to open the main valve, the main valve closes as a result of a return mechanism, and the flow is limited to the secondary flow passageway.
Various compound meters have been known in the art for measuring variable flow rates within a piping system. Such assemblies should accurately measure the flow rate over a wide range, while providing durability, reliability and a reasonable cost of manufacture. In particular, the meter should be accurate to within xe2x88x925% or +3% accuracy in all operations, including the range of operation where the meter switches primarily from measuring low flow to measuring high flow. This area of switching is known as the xe2x80x9ccrossover region.xe2x80x9d
In a compound meter of the prior art disclosed in Bradham, III et al., U.S. Pat. No. 4,100,799, a pivoting flap mechanism was used in the secondary flow passageway. During low flow, the flap would remain open. As flow increased, the flap closed and caused a pressure to build up which opened the valve in the primary passageway, after which the flap again opened to permit flow through the secondary passageway as well as through the main passageway at high flow rates.
It has been a technical goal to design an improved compound meter which is capable of economical manufacture in suitable quantities, and which does not require the flap mechanism. In test equipment, which did not use the flap, turbulent and uneven flow was encountered in the region where the secondary passageway exited the main flow passageway. This uneven flow produced inaccuracy outside of acceptable standards. In order to overcome this phenomenon, the present invention was made.
The invention is provided in a compound meter assembly in which a flow distributor is placed in the main passageway near a housing inlet and adjacent to the entrance to the secondary flow passageway from the main passageway. The flow distributor has a central opening for receiving the main flow and flow ports disposed around at least a portion of its circumference for allowing distributed portions of the main flow to flow towards interior walls of the housing such that the flow is better distributed across a cross section of the main passageway to maintain the accuracy of the meter at a crossover region between low flows being metered by the low volume flow meter and high flows being metered by the high volume flow meter.
In a preferred embodiment the flow distributor is provided by a ring-shaped member with equally sized apertures equally spaced around its circumference, however, it should be understood that other types of flow distributors are within the scope and spirit of the present invention.
In a preferred embodiment the housing is an integrally formed casting which contains the main passageway and includes an integrally formed side pipe that encloses a portion of the secondary passageway.
In a preferred embodiment, the high volume flow meter is of the turbine type, while the low volume flow meter is of the nutating disc type, however it should be understood that other types of metering elements could be used while still coming within the broadest scope of the present invention.
With the present invention, the compound meter will maintain accuracy to within a range between +3% and xe2x88x925% of actual flow rate even in the crossover region where the main valve is opening and primary metering is being switched from the low volume flow meter to the high volume flow meter. The meter also retains this accuracy when switching back from primary metering by the high volume flow meter to the low volume flow meter.
It is a further specific object of the invention to provide an improved simplified main valve configuration, such that the internal parts inside the meter housing have greater life, durability and reliability.
In particular, the valve is provided as a subassembly which conveniently screws into the meter housing.
Other objects and advantages, besides those discussed above, will be apparent to those of ordinary skill in the art from the description of the preferred embodiment which follows. In the description, reference is made to the accompanying drawings, which form a part hereof, and which illustrate examples of the invention. Such examples, however, are not exhaustive of the various embodiments of the invention, and, therefore, reference is made to the claims which follow the description for determining the scope of the invention.